What you'll need to make a Side Bag/Purse:
-Old bike tubes (26" or 29" are the widest. just ask for these at most any bike shop).
-Vinyl (I use old billboards. I called up Next Media and they gave me a few free ones).
-Lube (I used cooking oil because it's cheap, biodegradable, wipes off easy, and leaves a shiny coat).
-Most any sewing machine with a leather/denim needle and adjustable tension.
-Polyester thread
-Hot glue gun for tacking tube in place before sewing (optional, but makes it way easier/quicker. you can use clamps/safety pins too.)
-A clasp: i use a bike cog in this instructable. You could also use valcro, buckles, buttons, snaps, nothing - whatever.
-A strap: I use an old one ripped off another bag. Or you can make one out of seat belt, more tubes, etc.

Step 1: The Body

Tube
1) Cut 4 tube lengths of about 2'x4" (I usually cut a couple standard 26" tubes into 3rds to equal about this dimension. If you're a little off, oh well. see my "sewing bike tubes basics" instructable for how to do this.)
2) Sew together into a sheet (pictured). Don't worry about the tube lengths being a bit uneven.
3) Use a ruler (an 90 degree L shaped works quick) to draw straight lines at either end of the tubes - cut.

Vinyl
1) Lay tube sheet down on vinyl.
2) Trace tube sheet to back of vinyl using chalk or paint marker. Allow either end to be a half inch shorter than the tube sheet.

The machine did fine. There was a few broken denim needles and some weird thread tension when the layers got much - like sewing on the strap side loops. but besides that no problems. my best advice - lots of lube!